Conversion of fructose-containing feedstocks to HMF-containing product

ABSTRACT

The present invention relates generally to processes for converting fructose-containing feedstocks to a product comprising 5-(hydroxymethyl)furfural (HMF) and water in the presence of water, solvent and an acid catalyst. In some embodiments, the conversion of fructose to HMF is controlled at a partial conversion endpoint characterized by a yield of HMF from fructose that does not exceed about 80 mol %. In these and other embodiments, the processes provide separation techniques for separating and recovering the product, unconverted fructose, solvent and acid catalyst to enable the effective recovery and reutilization of reaction components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 14/606,789,filed Jan. 27, 2015, which claims benefit of U.S. provisionalapplication Ser. No. 61/932,185, filed Jan. 27, 2014, the entiredisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for convertingfructose-containing feedstocks, for example, high fructose cornsyrup-containing feedstocks, to a product comprising5-(hydroxymethyl)furfural (HMF) and water. In one aspect of theinvention, the process comprises the step of converting afructose-containing feedstock to HMF in a reaction zone in the presenceof water, solvent and acid catalyst to attain a relatively low specifiedyield of HMF at a partial conversion endpoint and thereafter theconversion of fructose to HMF is quenched at the partial conversionendpoint. Typically, the sum of unconverted fructose, HMF yield, and theyield of intermediates is at least 90 mol % at the partial conversionendpoint. In another aspect of the invention, the process comprisespartially converting the feedstock in a reaction zone in the presence ofwater, solvent and an acid catalyst, removing from the reaction zone thecombination resulting from the partial conversion, separatingunconverted fructose from the reaction combination removed from thereaction zone, and separating solvent separately from the separation ofthe unconverted fructose, the separations being conducted to enable thesubsequent recovery of product comprising HMF and water. The postreaction zone separations also enable the effective recovery andreutilization of unconverted fructose and solvent. In another aspect ofthe invention, selective membrane separation techniques are employed forthe separation and recovery of unconverted fructose and intermediatesfrom the desired product.

BACKGROUND OF THE INVENTION

HMF has been recognized as a chemical with potentially significantindustrial and commercial applications because of its high degree offunctionality and its ability to act as a precursor to variousindustrially useful chemicals. See Werpy, T; Petersen, G. (Eds.), “TopValue Added Chemicals from Biomass, Vol. 1: Results of Screening forPotential Candidates from Sugars and Synthesis Gas,” U.S. Dept. ofEnergy, Office of Scientific Information: Oak Ridge, Tenn.DOE/GO-102004-1992 (2004). For example, its functionality affords use inthe production of solvents, surfactants, pharmaceuticals and plantprotecting agents, and furan derivatives thereof which are useful asmonomers for the preparation of non-petroleum derived polymers.

HMF is primarily produced by dehydrating a carbohydrate feedstock,particularly monosaccharides such as glucose and fructose. Complicationscommonly arise during the reaction as a result of the production ofunwanted acid by-products, particularly levulinic and formic acid, andespecially the polymerization of reaction components which forms humins(a mixture of colored, soluble and insoluble oligomers and polymers),all of which reduce the overall process yield and complicate therecovery of HMF, making large scale production of HMF economicallyunattractive. These complications are exacerbated by the desire tomaximize conversion of feedstock to HMF in the reaction zone.

Fructose is the preferred hexose to produce HMF because it has beendemonstrated to be more amenable to dehydration reactions than otherhexoses including glucose. High fructose corn syrup (HFCS) is a highvolume, commercially available product from which HMF and other furanscould be produced in large quantities. Currently, as much as 18 billionpounds/yr of high fructose corn syrup are produced. Szmant et al, J.Chem. Tech. Biotechnology, Vol. 31, PP 135-45 (1981) disclosed the useof high fructose corn syrup as a feedstock for the production of HMF.

A variety of homogeneous catalysts have been employed to promote thedehydration of fructose to HMF. Inexpensive strong inorganic acids havebeen used: see, for example, U.S. Pat. No. 7,572,925. Organic acids havealso been disclosed, including relatively strong organic acids such asp-toluene sulfonic acid and weaker organic acids such as oxalic acid andlevulinic acid: See, for example, U.S. Pat. No. 4,740,605, whichdiscloses oxalic acid. All patents and other publications cited in thisapplication are incorporated herein by reference.

Similarly, a variety of heterogeneous catalysts have been reported asuseful for the dehydration of carbohydrate to HMF. See, for example deVries, Chem. Rev. 2013, pp1499-1597. Dumesic, ACS Catal 2012, 2,pp1865-1876; and Sandborn, U.S. Pat. No. 8,058,458. Fleche, in U.S. Pat.No. 4,339,387, disclosed the use of solid acid resin catalysts where theresin may be a strong or weak cationic exchanger, with thefunctionalization preferably being in the H⁺ form (including, forexample, resins under the trademark Amberlite C200 from Rohm & HaasCorporation and Lewatit SPC 108 from Bayer AG). Sanborn, in AU2011205116, disclosed that metals such as Zn, Al, Cr, Ti, Th, Zr and Vare useful as catalysts. And Binder, in US 2010/0004437 A1, disclosedthe use of a halide salt.

In addition to the use of catalysts in the dehydration of carbohydratesto HMF, there has been much focus on solvents and solvent systems thatreportedly are beneficial in the process. See for example, de VriesChem. Rev 2013, 113, 1499-1597.

A multitude of processes have been disclosed for the production of HMFfrom fructose. However, the known prior processes have not recognizedany benefit associated with low conversion in the reaction zone.Typically, research has focused on attaining the highest possibleconversion of fructose to HMF in the reaction zone, which inevitably hasresulted in increased off-path products, including humins, and/orprocess complexity and expense. In the quest to attain high conversionof fructose to HMF in the reaction zone, prior processes have focused onimproving catalyst performance, reactor solvent systems and reactantmixing techniques, using solvent modifiers to improve phase separationsin the reactor, using foam and/or oxidation suppressants, reducingcarbohydrate concentration in the reactor, using very high temperaturesand/or pressures, and performing multiple steps in the reactor (e.g.,steam injection or controlled vaporization to simultaneously removecertain constituents), among other techniques. Nevertheless, none of theprocesses disclosed to date appears to have overcome the low overallprocess productivity in a commercially economically viable manner.

In order to overcome the shortcomings of the prior processes, applicantshave discovered processes based upon intentionally limiting theconversion of fructose to HMF in the reaction zone. In these processes,HMF, unconverted fructose, solvent and, when applicable, catalyst areremoved from the reaction zone and ultimately separated from oneanother, enabling the efficient recycling of these separatedconstituents and, ultimately, the cost effective production and recoveryof large quantities of HMF.

SUMMARY OF THE INVENTION

Briefly, therefore, the present invention is directed to improvedprocesses for converting fructose-containing feedstocks to a productcomprising HMF and water.

In one embodiment, the process comprises combining fructose, water, anacid catalyst and a first solvent in a reaction zone and converting inthe reaction zone fructose to HMF and water and to intermediates to HMFto a partial conversion endpoint. The yield of HMF from fructose at thepartial conversion endpoint does not exceed about 80 mol %. At least aportion of the product, unconverted fructose and the first solvent areremoved from the reaction zone, as a combination, wherein the conversionof fructose to HMF in the combination removed from the reaction zone isquenched at the partial conversion endpoint. At least a portion of eachof the first solvent, the product and unconverted fructose in thecombination removed from the reaction zone are separated from oneanother. At least a portion of the separated unconverted fructose and atleast a portion of the separated first solvent are subsequently recycledto the reaction zone and the product comprising HMF and water isrecovered.

In accordance with another embodiment, the process comprises combiningfructose, water, an acid catalyst and at least a first solvent in areaction zone and converting in the reaction zone a portion of thefructose to HMF and water. At least a portion of the product,unconverted fructose and the first solvent are removed from the reactionzone as a combination and at least a portion of the combination iscontacted with a second solvent in a fructose separator to separate atleast a portion of unconverted fructose from the combination and producean intermediate composition having a reduced fructose concentration andcomprising the product and at least a portion of each of the firstsolvent and second solvent. At least a portion of the separated,unconverted fructose is recovered and at least a portion of the firstsolvent, the second solvent and the product in the intermediatecomposition are separated from one another.

In accordance with a further embodiment, the process comprises combiningfructose, water, an acid catalyst and at least a first solvent in areaction zone and converting in the reaction zone a portion of thefructose to HMF and water and to intermediates to HMF. At least aportion of the product, unconverted fructose, intermediates and firstsolvent are removed from the reaction zone as a combination and one ormore constituents of the combination withdrawn from the reaction zoneare separated by selective membrane separation.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 graphically illustrates a typical conversion of fructose to HMFin a reaction zone as a function of time, highlighting changes infructose, HMF and intermediate concentrations as well as changes inreaction mass balance, the latter of which is reflective of an increasedconcentration of off-path reaction products (including humins) at higherfructose conversions.

FIG. 2 depicts an example of a process flow diagram illustrating certainaspects of the present invention associated with the partial conversionof the fructose-containing feedstock to HMF, including separate solventand unconverted fructose separation steps, recovery of catalyst (whenapplicable) and recycling of some or all of these constituents to thereaction zone or elsewhere.

FIG. 3 depicts an example of a process flow diagram of a processemploying chromatographic separations technology (e.g., simulated movingbed technology) to effect separation of unconverted fructose andintermediates from the product comprised of HMF and water.

FIG. 4 depicts an example of a process flow diagram of a process whereina liquid-liquid extraction step is employed to separate initially, anddownstream of the reaction zone, at least a portion of the unconvertedfructose and intermediates from the combination withdrawn from thereaction zone.

FIG. 5 depicts an example of a process flow diagram of a process whereina liquid-liquid extraction step is employed to separate initially, anddownstream of the reaction zone, at least a portion of the unconvertedfructose and intermediates and wherein a second solvent is addeddownstream of the reaction zone to effect improved partitioning of HMFfrom unconverted fructose.

FIG. 6 depicts an example of a process flow diagram of an alternativeprocess configuration employing a liquid-liquid extraction step whereina polar solvent and non-polar solvent are added to the reaction zone andthe polar solvent is removed prior to a liquid-liquid extraction step toenable partitioning of HMF from unconverted fructose.

FIG. 7 depicts an example of a process flow diagram of a furtheralternative process configuration employing two solvents, one of whichis employed to provide enhanced partitioning in liquid-liquid extractionto enable portioning of HMF from unconverted fructose.

FIG. 8 depicts an example of a process flow diagram of a processconfiguration employing the use of ultra-filtration and nano-filtrationto enable the separation of HMF from unconverted fructose andintermediates.

FIG. 9 graphically illustrates the conversion of fructose to HMF in acontinuous flow reaction zone as a function of HCl concentration at afixed residence time, highlighting changes in fructose, HMF andintermediates concentrations.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, any of a variety offructose-containing feedstocks can be employed including, withoutlimitation, essentially pure fructose, sucrose, mixtures of glucose andfructose, and combinations thereof. Moreover, the present inventioncontemplates the use of starches, cellulosics and other forms ofcarbohydrates which, for example, are subjected to processing conditionsthat isomerize glucose produced from the starches or cellulosics to formfructose-containing feedstocks.

An aspect of the present invention is the partial conversion of afructose-containing feedstock to HMF. The conversion is carried out in areaction zone that contains at least fructose-containing feedstock,water, acid catalyst and solvent.

Water can be present in a reaction zone either as a separately addedconstituent or as a component of, for example, a solution offructose-containing feedstock. Conjunctively or alternatively, andwithout limiting the scope of the invention, water may be present in areaction zone as a solution comprised of a reaction modifier, such as anaqueous salt solution, as more fully described hereinafter.

Typically, an aqueous solution of fructose is used as the feedstock tothe reaction zone. In various preferred embodiments, commerciallyavailable high fructose corn syrup (HFCS) is dissolved in water to formthe solution. For example, HFCS-97 or HFCS-90 may be used.

The concentration of fructose in a reaction zone is generally in therange of from about 5 wt % to about 80 wt % dissolved solids. In variousembodiments, the concentration of dissolved solids is in the range ofabout 20 wt % to about 80 wt %. In various embodiments, theconcentration of dissolved solids is at least about 40 wt %. In someembodiments, it may be desirable to lower the concentration of fructosein the solutions to 20 wt % or less.

In accordance with the present invention the reaction takes place in areaction zone in the presence of an acid catalyst. The catalyst may be ahomogeneous or heterogeneous catalyst. Homogeneous catalysts includeBronsted or Lewis acids. Examples of such acids include organic andinorganic acids. Inorganic acids include mineral acids and other strongacids. Bronsted acids include HCl, HI, H₂SO₄, HNO₃, H₃PO₄, oxalic acidCF₃SO₃H and CH₃SO₃H. Lewis acids can include for example,borontrihalides, organoboranes, aluminum trihalides, phosphorus andantimony pentafluorides, rare earth metal triflates, and metal cationether complexes. Preferred acids are Bronsted acids selected from thegroup of HCl, HBr, H₂SO₄ and H₃PO₄. Quantities of catalyst whenhomogeneous are typically in the range of from about 0.1 to about 25mol. % vs. hexose, more typically from about 0.5 to about 10 mol. % orfrom about 0.5 to about 5 mol. %. Suitable heterogeneous catalystsinclude acid-functionalized resins, acidified carbons, zeolites, micro-and meso-porous metal oxides, sulfonated and phosphonated metal oxides,clays, polyoxometallates and combinations thereof. Preferredheterogeneous catalysts include acid functionalized resins. When aheterogeneous catalyst is employed, the catalyst loading in the reactionmixture will depend upon the type of reactor utilized. For example, in aslurry reactor, the catalyst loading may range from about 1 g/L to about20 g/L; in a fixed bed reactor the catalyst loading may range from about200 g/L to about 1500 g/L.

Also present in the reaction zone is a solvent. Solvents are typicallyorganic solvents and can either be polar or non-polar solvents.Generally, useful solvents can be selected from among ethers, alcohols,ketones and hydrocarbons. Examples of useful solvents include etherssuch diethyl ether, methyl tert-butyl ether, dimethoxyethane (DME orglyme), bis(2-methoxyethyl) ether (diglyme), tetrahydrofuran (THF),dioxane, and 2-methyltetrahydrofuran (MeTHF), ketones such as acetone,methyl ethyl ketone and methyl isobutyl ketone (MIBK), alcohols such asisopropanol, 2-butanol, and tert-butanol, and hydrocarbons such aspentane, hexane, cyclohexane and toluene. In various embodiments,solvents include DME, dioxane, THF, MeTHF, 2-butanol, and MIBK.

The fructose-containing feedstock, water, catalyst and solvent can existin the reaction zone as a mono- or multi-phasic system. The amount ofsolvent in the system relative to water typically ranges from 10:1 to1:1 on a mass basis. In various embodiments it can range from 5:1 to2:1. The presence of organic solvent in the reaction zone promotes bothfaster reaction rates and higher yields of HMF. Solvent-watercombinations that form either mono- or multi-phasic compositions in thereaction zone can be employed. Preferred solvents for the reaction zoneare unreactive under the conditions of fructose dehydration, and haveboiling points lower than water.

An important aspect of the invention is the partial conversion of thefructose in the reaction zone. That is, the dehydration reaction isallowed to proceed until a partial conversion endpoint is attained andthen the reaction is at least partially quenched (i.e., the conversionof fructose is reduced). In accordance with the present invention, theconversion of fructose in the reaction zone is controlled such that atthe partial conversion endpoint, the yield of HMF from fructose providedto the reaction zone is maintained at a relatively low specified yield.As discussed in greater detail below, applicants have discovered thatcontrolling the conversion of fructose to HMF at a specified yieldreduces conversion of HMF and/or fructose to off-path products such asoligomers and polymers produced from the reaction components andreferred to herein as humins, especially those which are soluble inwater or the solvent supplied to the reaction zone.

FIG. 1 graphically illustrates a typical conversion of fructose to HMFin a reaction zone as a function of time, highlighting changes infructose, HMF and intermediate concentrations as well as changes inreaction mass balance, the latter of which is reflective of an increasedconcentration of off-path reaction products (e.g., levulinic acid,formic acid, and soluble and insoluble humins) at higher fructoseconversions. Mass balance in this instance is defined as the sum ofunconverted fructose plus the mol % yield of HMF plus the mol % yield ofreaction intermediates. As discussed by István T Horvath et al.(Molecular Mapping of the Acid-Catlaysed Dehydration of Fructose, Chem.Commun., 2012, 48, 5850-5852), several different reaction pathways existfor the conversion of fructose to HMF as well as the generation ofvarious off-path products that are believed to lead to the formation ofhumins. On-path intermediates to HMF are reported to include isomers offructose such as α-D-fructofuranose and β-D-fructofuranose,2,6-anhydro-β-D-fructofuranose, fructofuranosyl oxocarbenium ions,(2R,3S,4S)-2-(hydroxymethyl)-5-(hydroxyl-methylene)-tetrahydrofuran-3,4-diol,(4S,5R)-4-hydroxy-5-hydroxymethyl-4,5-dihydrofuran-2-carbaldehyde anddifructose dianhydrides (DFAs). Off-path intermediates are reported toinclude (3S,4R,5R)-2-(hydroxymethylene)-tetrahydro-2H-pyran-3,4,5-trioland (3R,4S)-3,4-dihydroxy-3,4-dihydro-2H-pyran-6-carbaldehyde, which canbe converted to humins.

FIG. 1 also graphically depicts a typical conversion offructose-containing feedstock to HMF in accordance with the presentinvention, highlighting certain of the benefits attributable to partialconversion to HMF. More specifically, at time zero, no conversionoccurs. At time “t” (represented by the dashed line extending parallelto the yield axis, a 50% molar yield of HMF is produced throughconversion of fructose in the feedstock (as indicated by theintersection of the dashed line with the HMF yield line). Also, at time“t”, the concentration of fructose is significantly reduced (to about 30to about 35% of the starting concentration). Further, at time “t” inthis example, intermediates formation has effectively peaked. As to theformation of off-path product, including humins, applicants havediscovered that at a partial conversion of fructose to HMF characterizedby a relatively low specified yield of HMF (for example, as shown inFIG. 1 where the yield of HMF is about 50% or less at time “t”), thereaction to these undesired products is significantly reduced, asillustrated by the mass balance being >90% . Generally, off-path productat the partial conversion endpoint is maintained at not more than about10%, more typically not more than about 8%, in various embodiments doesnot exceed about 5% (as illustrated in FIG. 1), and in various preferredembodiments can be controlled so as not to exceed about 3%. Thus, in oneaspect of the invention the sum of unconverted fructose, the yield ofHMF from fructose and the yield of intermediates at the partialconversion endpoint should be at least about 90%, in various embodimentsat least about 92%, more typically at least about 95% and in variouspreferred embodiments at least about 97%.

As demonstrated in Example 7, the specified yield of HMF at the partialconversion endpoint can be suitably increased above 50% and still attainthe desired benefits of reduced production of off-path intermediates andimproved overall process yield of HMF. More particularly, in accordancewith the present invention, the conversion of fructose in the reactionzone is controlled such that at the partial conversion endpoint, theyield of HMF from fructose provided to the reaction zone is not morethan about 80%, not more than about 75%, not more than about 70%, notmore than about 65%, not more than about 60%, not more than about 55% ornot more than about 50%. For economic reasons, the yield of HMF in thereaction zone at the partial conversion endpoint is generally not lessthan about 30% and typically not less than about 40%. Thus, the yield ofHMF from fructose provided to the reaction zone at the partialconversion endpoint is generally controlled at from about 30 to about80%, from about 30 to about 75%, from about 30 to about 70%, from about30 to about 65%, from about 30 to about 60%, from about 30 to about 55%,from about 30 to about 50%, from about 40 to about 80%, from about 40 toabout 75%, from about 40 to about 70%, from about 40 to about 65%, fromabout 40 to about 60%, from about 40 to about 55%, from about 40 toabout 50% or from about 40 to about 45%. On the other hand, the upperend of the HMF yield at the partial conversion endpoint will depend onvarious factors, including the nature and concentration of the catalyst,water concentration, solvent selection and other factors that caninfluence the generation of off-path products. Generally, operationwithin the ranges for HMF yield at the partial conversion endpoint asdisclosed herein are consistent with the adequate control of theproduction of off-path intermediates while maintaining desired overallprocess yield of HMF.

In accordance with various embodiments of the invention, to effectpartial conversion, the reaction zone is generally maintained at atemperature in the range of from about 50° C. to about 250° C., moretypically in the range of from about 80° C. to about 180° C. Generally,higher temperatures increase the reaction rate and shorten the residencetime necessary to reach the partial conversion endpoint. The reactionconstituents within the reaction zone are typically well-mixed toenhance the conversion rate and the zone is typically maintained at apressure in the range of from about 1 atm to about 15 atm or from about2 atm to about 10 atm. In various embodiments, the temperature andpressure within the reaction zone are maintained such that theconstituents in the reaction zone are largely maintained in the liquidphase. The pressure in the reaction zone can be maintained by supplyingan inert gas such as nitrogen.

The time during which the reaction is carried out in the reaction zoneprior to the partial conversion endpoint and before quenching theconversion of fructose and removal of materials from the zone isvariable depending upon the specific reaction conditions employed (e.g.,reaction temperature, the nature and quantity of the catalyst, solventselection, water concentration in the reaction zone, etc.) and generallycan range from about 1 to about 60 minutes. The composition of thereaction mixture with respect to HMF yield from fructose and theconcentration of intermediates to HMF from fructose and of unconvertedfructose can be monitored using various means known to those skilled inthe art to determine and establish the desired partial conversionendpoint in accordance with the present invention. For example, periodicsampling and analysis (e.g., by HPLC) of the reaction zone materials isbut one of several ways to determine and establish the partialconversion endpoint. Additionally or alternatively, the composition ofthe reaction mixture may be monitored using the dehydration reactionmass balance, wherein a decrease in the mass balance is reflective of anincreased concentration of off-path reaction products (including humins)and thus a commensurate decrease in the sum of unconverted fructose, theyield of HMF from fructose and the yield of intermediates. The partialendpoint control method can be integrated into a programmed processcontrol scheme based on an algorithm generated using historicalanalytical data, and can be updated by on-line or off-line analyticaldata.

Once the desired partial conversion endpoint is attained, thedehydration reaction and conversion of fructose is typically at leastpartially quenched to avoid significant additional production of anyoff-path products (e.g., levulinic acid, formic acid, and soluble andinsoluble humins). Typically, at least a portion of the combinationproduced in the reaction zone is withdrawn for subsequent processing andproduct recovery as described in detail below. In these and otherembodiments, the conversion of fructose can be suitably quenched afterthe partial conversion endpoint is attained by reducing the temperatureof the reaction constituents either within the reaction zone or afterbeing withdrawn from the zone using various industrial means known tothose skilled in the art. For example, and without limitation, thereaction constituents may be cooled by flash evaporation, contact with acooling inert gas, mixing with a liquid diluent, passage through anindirect heat exchanger or a combination of these and other techniques.Typically, in such embodiments, the reaction constituents are cooled toa temperature below about 100° C., more typically, below about 60 or 50°C. It should be understood that other means for quenching the conversionof fructose may be employed without departing from the presentinvention. For example, in embodiments where a heterogeneous catalystthat is retained in the reaction zone (e.g., a fixed bed catalyst) isemployed, the conversion of fructose at the partial conversion endpointcan be quenched by withdrawing some or all of the combination producedfrom the reaction zone.

FIG. 2 illustrates basic process steps employed for the partialconversion of fructose-containing feedstocks to HMF in accordance withthe present invention. As illustrated in FIG. 2, feedstock is added asan aqueous solution to the reaction zone, or feedstock and water may beadded separately. Additionally, catalyst (heterogeneous or homogeneous)is added to the reaction zone. In the case of a heterogeneous catalyst,the catalyst is typically added to the reaction zone prior to theaddition of the feedstock, water and solvent. In the case of ahomogeneous catalyst, the catalyst may be pre-mixed with the feedstockand/or solvent before being supplied to the reaction zone (see FIG. 3 etseq.) or may be added before, simultaneously with or after thefeedstock, water and/or solvent is added to the reaction zone. Further,solvent may be added to the reaction zone before, simultaneously with orafter addition to the reaction zone of one or more of the other reactionzone constituents. Again, in various embodiments of the presentinvention, regardless of the order in which the constituents areprovided to the reaction zone, some or all of the reaction constituentsmay be mixed prior to addition to the reaction zone or mixed in thereaction zone, all so as to enhance the conversion rate in the reactionzone. Mixing can be undertaken by any of a variety of means well knownin the art.

In accordance with the present invention, the conversion step can becarried out in one or more reaction zones. For illustrative purposes,the figures depict only one reaction zone. The process may be carriedout in batch, semi-continuously or substantially continuous manner. Anyof a variety of well known reactor designs defining at least onereaction zone is suitable for carrying out the process of the presentinvention. For example, and without limitation, useful reactors includetank reactors, continuously stirred tank reactors (CSTRs), flow throughcontinuous reactors, fixed bed continuous reactors, slurry type reactorsand loop reactors, among others. Single reactors may be employed orcombinations of several reactors. Again, reactors may comprise one ormore reaction zones. Multiple reaction zones in series may be employedusing, for example, cascading tank reactors or continuous reactors, orone continuous reactor provided with multiple, separated reaction zones.Those of ordinary skill in the art will appreciate the multitude ofreactor configurations which may be employed to achieve the objectivesof the present invention.

The output from the reaction zone is a combination comprising HMF,unconverted fructose, intermediates produced during the conversion step,solvent, water and off-path products which may result from theconversion step. Additionally, when homogeneous catalyst is employed,the output from the reactor will include catalyst. Output from thereactor (i.e., the combination removed from the reaction zone at thepartial conversion endpoint) includes, quantitatively, at least someamount of each constituent provided to the reaction zone (excludingcatalyst, other than impurity amounts, in embodiments in which fixed bedheterogeneous catalysts are employed). For example, in an embodimentemploying a tank reactor, the entire contents of the reactor (again, thecombination) may be removed after the partial conversion endpoint isattained. Alternatively, for example, in embodiments employingcontinuous flow reactors, only a portion of the contents in the reactionzone (again, the combination) may be removed in a given period of timeto establish a minimum reactor residence time necessary to attain atarget partial conversion endpoint.

FIG. 3 illustrates an embodiment of the partial conversion process ofthe present invention using a homogeneous catalyst and employing acombination of a solvent separator 300, a catalyst recovery unit 500,and a product recovery unit 600 to separate and remove unconvertedfructose and intermediates from the desired product, HMF in water, andenable recycling of certain reaction constituents. In this embodiment,an aqueous stream of fructose-containing feedstock is supplied via 301to mixer 100 for mixing reaction constituents (e.g., a stirred tank).Also provided to mixer 100 via 302 is fresh and make up solvent, watervia 303, and catalyst via 304. In this embodiment, catalyst may also beprovided to a reaction zone 200 via 304 a. As contemplated in FIG. 3,supply of catalyst to mixer 100 and reaction zone 200 need not beexclusive to either; instead, it may be supplied to both. The mixedreaction constituents are supplied to the reaction zone via 305. In thereaction zone 200, fructose is converted to HMF until the partialconversion endpoint is attained and then the conversion reaction issuitably quenched as described above. At least a portion of the reactionconstituents, product (HMF and water), intermediates to HMF, solvent (inthis embodiment the solvent is preferably polar) and off-path products(such as levulinic acid, formic acid, and soluble and insoluble humins,among others) are removed from the reaction zone as a combination andsupplied via 306 to solvent separator 300 for separating at least aportion of solvent from the combination. In embodiments where theboiling point of the solvent is significantly lower than the othercomponents of the combination, a simple evaporative separation may becarried out and the heat of vaporization may optionally be used to coolthe reaction components in quenching the conversion of fructose.However, in embodiments where, for example, the boiling point of thesolvent is relatively close to (whether above or below) that of othercomponents of the combination, a distillation unit may be utilizedwherein a fraction composed substantially of solvent and some water,preferably essentially only solvent, can be withdrawn at an appropriatelocation along the length of the column. Separated solvent is typicallycondensed to a liquid phase and preferably, as illustrated for examplein FIG. 3, supplied via 307 as a component of the recycled mixtureprovided to the mixer 100 via 311 c. In various embodiments, partialsolvent separation is preferred as it may be advantageous in assistingthe separation of fructose from the product.

The remaining constituents from the combination withdrawn from reactionzone 200 are delivered via 308 to a filtration unit 400. In filtrationunit 400 insoluble, typically solid, humins are removed from the stream308 and disposed of via 308 a. The remaining liquid from filtration unit400 is delivered via 309 to catalyst recovery unit 500 (e.g., an ionexchange unit) designed, for example when HCl or H₂SO₄ is the catalyst,to capture the chloride or sulfate ions on the exchange resin prior tothe separation of the unconverted fructose from the product. The“catalyst free” eluent from the catalyst recovery unit 500 is suppliedvia 310 to product recovery unit 600, which in the illustratedembodiment is a continuous chromatographic separation (e.g., simulatedmoving bed, liquid chromatography or, for short, SMB) unit in which thetypically more difficult separation of the unconverted fructose from theproduct is carried out. SMB units are well known to those of ordinaryskill in the art of separations; for example, SMB units are industriallyemployed in the separation of similar products such as, for example,glucose from fructose. In operation, water is added to the bed via 312and the mixture of HMF, unconverted fructose and water flows through themultiple columns of the SMB unit to separate HMF from fructose.Ultimately, not more than about 10%, typically not more than about 5%,or not more than about 2% of the unconverted fructose is unseparatedfrom the HMF. The product is removed via 313 and the unconvertedfructose is removed via 311. Optionally, a purge stream 311 a isprovided to remove some of the collected, unconverted fructose and waterfor any of variety of purposes including, for example, testing, use inanother reaction train, to maintain process water balance or for otherpurposes. The remainder, stream 311 b, can be combined with recoveredsolvent from stream 307 and resupplied to mixer 100 ultimately as aconstituent of recycle stream 311 c.

FIG. 4 illustrates an embodiment of the partial conversion process ofthe present invention using a homogeneous catalyst and employing acombination of a fructose separator 700 for separating unconvertedfructose from the combination removed from the reaction zone, forexample, by employing liquid-liquid extraction technology, a catalystrecovery unit 500, a solvent separator 300, and a filter 400 forremoving off-path products such as insoluble humins from product. Inthis embodiment, an aqueous stream of fructose-containing feedstock issupplied via 401 to mixer 100 for mixing reaction constituents (e.g., astirred tank). Also provided to mixer 100 via 402 is fresh and make upsolvent, water provided via 403, and catalyst via 404. In thisembodiment, catalyst may also be provided to a reaction zone 200 via 404b. As contemplated in FIG. 4, supply of catalyst to mixer 100 andreaction zone 200 need not be exclusive to either; instead, it may besupplied to both. The mixed reaction constituents are supplied to thereaction zone via 405. In the reaction zone 200, fructose is convertedto HMF until the partial conversion endpoint is attained and then theconversion reaction is suitably quenched as described above. At least aportion of the reaction constituents, product (HMF and water),intermediates to HMF, solvent (in this embodiment the solvent may bepolar or non-polar, preferably polar) and off-path products (such aslevulinic acid, formic acid, and soluble and insoluble humins, amongothers) are removed from the reaction zone in combination and suppliedvia 406 to fructose separator 700 for separating unconverted fructosefrom the combination removed from the reaction zone.

In one embodiment, fructose separator 700 is a liquid-liquid extractionapparatus. This separation method is well known and encompassesestablishing conditions that enable partitioning of one or moreconstituents into one layer (phase) preferentially as compared toanother layer (phase) that forms in the vessel as a result of conditionsestablished therein. Partitioning can be achieved by, for example,choosing an appropriate solvent or by adding to fructose separator 700 acomposition of matter that promotes the partitioning. It has beenproposed in US 2010/0004437 A1 that unconverted fructose can beextracted from a reaction product comprised of HMF, solvent and water byadding salts such as for example NaCl or MgCl₂. In some embodiments, thesolvent used to extract unconverted fructose can be used as a coolingmedium to quench the conversion of fructose.

An unexpected advantage of embodiments of the present invention in whichliquid-liquid separation is employed is that the homogeneous acidcatalyst is readily recovered and easily resupplied to the reaction zonewith, for example, the unconverted fructose. The partitioned unconvertedfructose and at least a portion of the acid catalyst are removed via407. A part of the partitioned unconverted fructose may optionally bepurged via 407 a for any of a variety of reasons. For example, a portionof the water that may have been partitioned with the unconvertedfructose may be separated, for example, by using an evaporator and theunconverted fructose with reduced water content returned to the reactionzone to maintain water balance. Ultimately, not more than about 10%,typically not more than about 5%, or not more than about 2% of theunconverted fructose remains in the liquid fed via 408 to catalystrecovery unit 500.

The remaining constituents partitioned in the other layer (in thisembodiment comprising product, catalyst, any partitioning additive andsolvent are delivered via 408 to catalyst recovery unit 500 (e.g., anion exchange unit) designed, for example when HCl or H₂SO₄ is thecatalyst, the capture the residual chloride or sulfate ions on theexchange resin prior to isolation of the product. In this embodiment itis anticipated that at least a portion, more preferably essentially all,of the homogeneous catalyst is separated during the liquid-liquidextraction process. The catalyst is separated into the phase containingthe unconverted fructose and consequently may be recovered and recycledto the reaction zone. The “catalyst free” eluent from the ion exchangeunit 500 is supplied via 409 to the solvent separator 300 for separatingsolvent(s) from the remaining constituents of the combination. Inembodiments where the boiling point of the solvent is significantlylower than the other components of the combination, a simple evaporativeseparation may be carried out; however, in embodiments where, forexample, the boiling point of the solvent is relatively close to(whether above or below) that of other components of the combination, adistillation unit may be utilized wherein a fraction composedsubstantially of solvent and some water, preferably essentially onlysolvent, can be withdrawn at an appropriate location along the length ofthe column. Separated solvent is preferably, as illustrated in FIG. 4,supplied via 410 as a component of the recycled mixture provided to themixer 100 via 410 a. The remaining constituents from the combinationwithdrawn from the solvent separator 300 via means 411 are delivered via411 a, optionally with additional water supplied via 412, to filter 400.In filter 400 insoluble, typically solid, humins are removed from thestream 411 a and disposed of via 413. The product is removed from thefilter 400 via 414. The unconverted fructose stream 407 b (and catalystrecovered from the liquid-liquid separation) is mixed with recoveredsolvent from stream 410 to form stream 410 a which is resupplied to themixer 100.

FIG. 5 illustrates a preferred embodiment of the partial conversionprocess of the present invention using an homogeneous catalyst andemploying two solvents, one of which is employed to provide enhancedpartitioning in fructose separator 700 for separating unconvertedfructose from the combination removed from the reaction zone, forexample, by employing liquid-liquid extraction technology. Theconfiguration of major aspects of the process illustrated in FIG. 5 isthe same as illustrated in FIG. 4. In this embodiment, an aqueous streamof fructose-containing feedstock is supplied via 501 to mixer 100 formixing reaction constituents (e.g., a stirred tank). Also provided tomixer 100 via 502 is fresh and make up solvent, water provided via 503,and catalyst via 504. In this embodiment, catalyst may also be providedto a reaction zone 200 via 504 a. Supply of catalyst to mixer 100 andreaction zone 200 need not be exclusive to either; instead, it may besupplied to both. The mixed reaction constituents are supplied to thereaction zone via 505. In the reaction zone 200, fructose is convertedto HMF until the partial conversion endpoint is attained and then theconversion reaction is suitably quenched as described above. At least aportion of the reaction constituents, product (HMF and water),intermediates to HMF, solvent (in this embodiment the solvent may bepolar or non-polar, preferably polar) and off-path products (such aslevulinic acid, formic acid, and soluble and insoluble humins, amongothers) are removed from the reaction zone in combination and suppliedvia 506 to fructose separator 700 for separating unconverted fructosefrom the combination.

In one embodiment, fructose separator 700 is a liquid-liquid extractionapparatus. In this embodiment, a second solvent is added via 507 to theextractor 700. It is known to those skilled in the art that addition ofa second solvent will affect the partition coefficient of the solublecomponents. The partitioned unconverted fructose and separated catalystis removed via 508 and recycled to the mixer 100 as described in moredetail hereinafter. A part of the partitioned unconverted fructose mayoptionally be purged via 508 a as described above with respect to FIG.4. Ultimately, not more than about 10%, typically not more than about5%, or not more than about 2% of the unconverted fructose is containedin the liquid fed via 509 to catalyst recovery unit 500.

The remaining constituents partitioned into the layer that is the stream509 (comprising product, catalyst, most or all of both solvents andoff-path products) are delivered to catalyst recovery unit 500 (e.g., anion exchange unit) designed, for example when HCl or H₂SO₄ is thecatalyst, to capture the residual chloride or sulfate ions on theexchange resin prior to further processing steps. The “catalyst free”eluent from the ion exchange unit 500 is supplied via 510 to the solventseparator 300 for separating the solvents from the remainingconstituents of the combination. In this embodiment, a distillation unitis utilized wherein fractions composed substantially of the firstsolvent and some water, preferably essentially only the first solvent, afraction composed substantially of the second solvent and some water,preferably essentially only the second solvent, and a bottoms fractioncomprised of product and off-path product can be withdrawn atappropriate, different locations along the length of the column. Asillustrated in FIG. 5, separated first solvent is supplied via 511 as acomponent of the recycled mixture provided to the mixer 100 via 511 a.Separated second solvent is recovered via 512 and supplied to thefructose separator 700 as, for example, a component of stream 506 a (asshown) or directly to fructose separator 700 (not illustrated). Theremaining product and off-path products withdrawn from solvent separator300 via 513 are delivered via 513 a, optionally with additional watersupplied via 514, to filter 400. In filter 400 insoluble humins andother off-path products are removed from the stream 513 a and disposedof via 515. The product is removed from the filter 400 via 516. Theunconverted fructose stream 508 b (and recovered catalyst) is then mixedwith recovered first solvent stream 511 to form stream 511 a which isresupplied to the mixer 100.

FIG. 6 illustrates an embodiment of the partial conversion process ofthe present invention using a homogeneous catalyst and employing twosolvents, wherein both solvents are supplied to the reaction zone. Inthis embodiment, the configuration of major aspects of the process isdifferent from that which is illustrated in FIG. 5 in that two solventseparators 300 and 300 a are provided wherein one solvent separator 300is provided upstream of fructose separator 700 to separate the firstsolvent from the combination removed from the reaction zone via 607 andanother solvent separator 300 a (which may be the same, similar to ordifferent from solvent separator 300) provided downstream of fructoseseparator 700. In this embodiment, an aqueous stream offructose-containing feedstock is supplied via 601 to mixer 100 formixing reaction constituents (e.g., a stirred tank). Also provided tomixer 100 via 602 is fresh and make up first solvent, water provided via603, and catalyst via 604. In this embodiment, catalyst may also beprovided to a reaction zone 200 via 604 a. Fresh and make-up secondsolvent is supplied to the reaction zone via 606. Although notillustrated, it will be apparent to those skilled in the art that thesecond solvent could be provided to the mixer 100. Supply of catalyst tomixer 100 and reaction zone 200 need not be exclusive to either;instead, it may be supplied to both. The mixed reaction constituents aresupplied to the reaction zone via 605. In the reaction zone 200,fructose is converted to HMF until the partial conversion endpoint isattained and then the conversion reaction is suitably quenched asdescribed above. At least a portion of the reaction constituents,product (HMF and water), intermediates to HMF, solvent (in thisembodiment the solvent may be polar or non-polar, preferably polar) andoff-path products (such as levulinic acid, formic acid, and soluble andinsoluble humins, among others) are removed from the reaction zone incombination and supplied via 607 to solvent separator 300 for separatingat least a portion of the first solvent from the combination removedfrom the reaction zone. The separated first solvent is removed via 608to be resupplied to the mixer 100 as a component of stream 614 b. Theremainder from the solvent separator 300 is removed via 609 and suppliedto fructose separator 700 for separating unconverted fructose from thecombination removed from the reaction zone.

In one embodiment, fructose separator 700 is a liquid-liquid extractionapparatus. In this embodiment, the partitioned unconverted fructose (andcatalyst) is removed via 610 and recycled to the mixer 100 as describedin more detail hereinafter. Optionally, a purge may be affected via 610a to remove a portion of the unconverted fructose for any of a varietyof reasons. Also, for example, means may be provided (not illustrated)to remove, for example, by another separation means (such as for exampleevaporation), a portion of the water that may have been partitioned withthe unconverted fructose. Ultimately, not more than about 10%, typicallynot more than about 5%, or not more than about 2% of the unconvertedfructose is contained in the liquid fed via 611 to catalyst recoveryunit 500.

The remaining constituents partitioned into the layer that is stream 611(in this embodiment product, residual catalyst, the second solvent andoff-path products) are delivered to catalyst recovery unit 500 (e.g., anion exchange unit) designed, for example when HCl or H₂SO₄ is thecatalyst, to capture the residual chloride or sulfate ions on theexchange resin prior to further processing steps. The “catalyst free”eluent from the ion exchange unit 500 is supplied via 612 to solventseparator 300 a for separating the second solvent from the remainingconstituents of the combination. In this embodiment, a distillation orevaporation unit may be utilized depending upon the boiling point of thesecond solvent relative to that of the product wherein a fractioncomposed substantially of the second solvent and some water, preferablyessentially only the second solvent, is removed via 614 and recycled tomixer 100 as a component of the constituents supplied via 614 a and 614b to the mixer 100. The remaining product and off-path productswithdrawn from the solvent separator 300 a via means 613 are delivered,optionally with additional water supplied via 613 a, to filter 400. Infilter 400 insoluble humins are removed from the filter 400 as a stream615 which may be disposed. The product is removed from the filter 400via 616. The unconverted fructose containing stream 610 b (and separatedcatalyst) is mixed with recovered second solvent and supplied via 614 ato mix with recovered first solvent containing stream 608 to form stream614 b which is resupplied to mixer 100.

FIG. 7 illustrates another preferred embodiment of the partialconversion process of the present invention using a homogeneous catalystand employing two solvents, one of which is employed to provide enhancedpartitioning in fructose separator 700 for separating unconvertedfructose, catalyst and intermediates from the product. In thisembodiment, an aqueous stream of fructose-containing feedstock issupplied via 701 to mixer 100 for mixing reaction constituents (e.g., astirred tank). Also provided to mixer 100 via 702 is fresh and make upfirst solvent. Water is provided via 703 and catalyst is supplied via704 and/or 704 b. The mixed reaction constituents are supplied to thereaction zone via 705. In the reaction zone 200, fructose is convertedto HMF until the partial conversion endpoint is attained and then theconversion reaction is suitably quenched as described above. At least aportion of the reaction constituents, product (HMF and water),intermediates to HMF, solvent (in this embodiment the solvent may bepolar or non-polar, preferably polar) and off-path products (such aslevulinic acid, formic acid, and soluble and insoluble humins, amongothers) are removed from the reaction zone in combination and suppliedvia 706 to solvent separator 300 for separating at least a portion(preferably, substantially all) of the first solvent from the reactioncombination. The solvent separation technique employed may be selectedfrom among many options known to those skilled in the art (e.g., flashevaporation). The first solvent is removed as stream 707 for resupply tomixer 100 as a component of stream 710 c.

The remaining constituents are removed from the first solvent separator300 as stream 708. A second solvent, which is different from the firstsolvent, is added to stream 708 via 713. For example, in thisembodiment, the first solvent can be an ether, such as DME and thesecond solvent can be a ketone, such as MIBK. The resulting stream 709is supplied to fructose separator 700. Fructose separator 700 is aliquid-liquid extraction apparatus and separates a liquid phasecomprising unconverted fructose, intermediates and catalyst from thecomposition of the stream 709. The partitioned liquid phase comprisingunconverted fructose, intermediates and separated catalyst is removedvia 710 and recycled to mixer 100 as described in more detailhereinafter. Optionally, a part of the liquid for any of a variety ofreasons may be purged via 710 a. For example, means may be provided (notillustrated) to remove, for example, by another separation means (suchas for example evaporation), a portion of the water that may have beenpartitioned with the unconverted fructose.

The remaining constituents partitioned into the layer that is the stream711 (comprising product, some catalyst, preferably substantially all ofthe second solvent and off-path products) are delivered to catalystrecovery unit 500 (e.g., an ion exchange unit) designed, for examplewhen HCl or H₂SO₄ is the catalyst, to capture the residual chloride orsulfate ions on the exchange resin prior to further processing torecover product. Ultimately, not more than about 10%, typically not morethan about 5%, or not more than about 2% of the unconverted fructose iscontained in the liquid fed via 711 to the ion exchange unit 500. Uponeffecting ion exchange to capture substantially all of the remainingcatalyst, the “catalyst free” eluent from the ion exchange unit 500 issupplied via 712 to a second solvent separator 300 a for separating thesecond solvent from the product. In this embodiment, a flash evaporationunit may be utilized to vaporize the second solvent and some water,preferably essentially only the second solvent. The bottoms fraction,now comprised of product and off-path materials can be withdrawn via714. As illustrated in FIG. 7, separated first solvent from solventseparator 300 is supplied via 710 b as a component of the recycledmixture provided to mixer 100 via 710 c. Separated second solvent fromsecond solvent separator 300 a is recovered via 713 and resupplied tothe fructose separator 700. Make-up second solvent, if needed, may beadded via 713 a. The remaining product and off-path materials withdrawnfrom second solvent separator 300 a via 714 are delivered via 716,optionally with additional water supplied via 715, to filter 400. Infilter 400 insoluble humins and other off-path materials are removed anddisposed of via 718. The product is then removed from the filtrationunit 400 as stream 717. The unconverted fructose containing stream 710 b(and separated catalyst) is then mixed with recovered first solventstream 707 to form stream 710 c which is resupplied to mixer 100.

In another aspect of the invention, selective membrane separationtechniques (e.g., ultra-filtration and/or nano-filtration) are employedto separate unconverted fructose, intermediates and HMF from the otherconstituents of the combination withdrawn from the reaction zone.Selective membrane separation techniques utilized to treat the aqueouscombination withdrawn from the reaction zone as disclosed herein provideeffective recovery of unconverted fructose and intermediates forrecycle, increased overall process yields and a high degree of productrecovery.

FIG. 8 illustrates another embodiment of the partial conversion processof the present invention using a homogeneous catalyst and an employingultra-filtration unit 300 for the removal of humins, and anano-filtration unit 500 for the separation of unconverted fructose andintermediates from the desired HMF product to enable the recycling ofcertain reaction constituents back to the reaction zone 200.

An aqueous stream of fructose-containing feedstock is supplied via 801to mixer 100 for mixing reaction constituents (e.g., a stirred tank).Also provided to mixer 100 via 802 is fresh and make up solvent. Wateris optionally provided via 803 and catalyst is supplied via 804 and/or804 b. The mixed reaction constituents are supplied to the reaction zone200 via 805. In the reaction zone 200, fructose and reactionintermediates are converted to HMF until the partial conversion endpointis attained and then the conversion reaction is suitably quenched asdescribed above. At least a portion of the reaction constituents,product (HMF and water), intermediates to HMF, solvent (in thisembodiment the solvent may be polar or non-polar, preferably polar) andoff-path products (such as levulinic acid, formic acid, and soluble andinsoluble humins, among others) are removed from the reaction zone incombination via 806 and subjected to selective membrane separationtreatment as described in detail below.

The aqueous combination removed from the reaction zone intended forselective membrane separation treatment may be collected in an optionalfeed tank (not shown). In order to prevent fouling and the resultingloss of flux and extend the useful life of the selective membrane(s)employed in membrane separation unit(s), the suspended solids content inthe aqueous combination removed from the reaction zone is optionallycontrolled. Typically, the aqueous combination will contain less thanabout 10,000 ppm of suspended solids. To enhance membrane performanceand extend membrane life, the suspended solids content of the aqueouscombination subjected to membrane separation may be reduced to less thanabout 1000 ppm, less than about 500 ppm, or less than about 100 ppm. Thesolids content of the aqueous combination removed from the reaction zonein 806 can be reduced, as necessary, to the desired level in an optionalsolids reduction stage (not shown). The solids reduction stage mayrepresent a point of dilution wherein the aqueous combination is dilutedwith a quantity of an aqueous diluent (e.g., process water).Alternatively, the solids content of the aqueous combination can bereduced by a conventional filtration operation. The filtration operationcan be suitably conducted in a batch mode (e.g., using bag filters) orin a continuous mode allowing for continuous flow of the aqueouscombination through the solids reduction stage. Suitable continuousfilters include cross-flow filters and continuous back-pulse filterswherein a portion of the filtrate is used to periodically back-pulse thefilter media to dislodge and remove separated solids. Typically, thefilter media employed is capable of separating and removing suspendedsolids greater than about 250 μm in size from the aqueous combination.It should be understood that any optional solids reduction stage maycomprise a combination of dilution, filtration and/or other operationsto attain the desired solids content in the aqueous combination prior toselective membrane separation treatment. The suspended solids content ofthe aqueous combination removed from the reaction zone can be readilydetermined by analytical methods known in the art such as by turbiditymeasurement (e.g., nephelometric turbidity units or NTU) and correlationof the turbidity reading to a known standard or by other methods knownto those skilled in the art.

Following optional suspended solids reduction, the aqueous reactioncombination withdrawn from the reaction zone is supplied via 806 toultra-filtration unit 300 in which the aqueous reaction combination iscontacted with one or more ultra-filtration membranes to produce aconcentrate or retentate stream 807 containing at least a portion(preferably, substantially all) of the humins from the reactioncombination and a permeate stream 810 containing unconverted fructose,intermediates, catalyst and HMF and depleted in humins relative to theaqueous reaction combination. Stream 807 is then fed to a solventrecovery unit 400 for the recovery of solvent from the humins-containingretentate stream. The humins are isolated via stream 808 and therecovered solvent stream 809 may be combined with stream 816 andsupplied as diluents stream 816 a to the downstream nano-filtration unit500 as described below.

The ultra-filtration permeate stream 810 in combination with diluentstream 816 a is supplied to nano-filtration unit 500 and contacted withone or more nano-filtration membranes to produce a permeate stream 811containing HMF product, solvent and water and a retentate stream 812containing at least a portion (preferably, substantially all) of theunconverted fructose and intermediates. Nano-filtration retentate stream812 may also contain some portion of HMF and catalyst (i.e., homogeneouscatalyst, if present) that did not permeate the nano-filtration unit500. Nano-filtration permeate stream 811 may also contain catalyst, andsome residual amounts of humins, fructose and reaction intermediatesthat have passed through the ultra-filtration and nano-filtration units.Stream 812 is supplied to mixer 100 for recycle to reaction zone 200.

The ultra-filtration unit 300 and nano-filtration unit 500 may compriseone or more ultra-filtration or nano-filtration membranes or modules andmay be configured as either a single pass or multi-pass system,typically in a cross-flow arrangement wherein the feed flow is generallytangential across the surface of the membrane. The membrane modules maybe of various geometries and include flat (plate), tubular, capillary orspiral-wound membrane elements and the membranes may be of mono- ormultilayer construction. In some embodiments, tubular membrane modulesmay allow for higher solids content in the mother liquor solution to betreated such that solids reduction upstream of the membrane separationunit is not required or can be significantly reduced. The separationmembranes and other components (e.g., support structure) of the membranemodules are preferably constructed to adequately withstand theconditions prevailing in the feed mixture and the membrane separationunit. For example, the separation membranes are typically constructed oforganic polymers such as crosslinked aromatic polyamides in the form ofone or more thin film composites. Specific examples of suitableultra-filtration membranes include, for example and without limitation,spiral wound GE UF membranes having a molecular weight cut-off (MWCO) of1000 available from GE Water & Process Technologies, Inc. (Trevose,Pa.), a division of GE Power & Water. Specific examples of suitablenano-filtration membranes include, for example and without limitation,spiral wound Dairy NF membranes having a MWCO of 150 and spiral wound Hseries membranes having a MWCO of 150-300 available from GE Water &Process Technologies, Inc.

Selective membrane separation techniques such as ultra-filtration andnano-filtration are pressure-driven separation processes driven by thedifference between the operating pressure and the osmotic pressure ofthe solution on the feed or retentate side of a membrane. The operatingpressure within a membrane separation unit will vary depending upon thetype of membrane employed, as osmotic pressure is dependent upon thelevel of transmission of solutes through the membrane. Operatingpressures in the membrane separation unit are suitably achieved bypassing the feed stream (e.g., incoming reaction constituents in thecombination removed from the reaction zone) through one or more pumpsupstream of the membrane unit, for example, a combination booster pumpand high-pressure pump arrangement. Generally, ultra-filtrationoperations exhibit lower osmotic pressures than nano-filtrationoperations, given the same feed solution. The driving force fortransmission through the membrane (i.e., permeate flux) increases withthe operating pressure. However, the benefits of increased operatingpressure must be weighed against the increased energy (i.e., pumping)requirements and the detrimental effects (i.e., compaction) on membranelife.

Typically, the operating pressure utilized in the ultra-filtrationoperation is less than about 800 kPa absolute and preferably from about200 to about500 kPa absolute. Typically, the operating pressure utilizedin the nano-filtration operation is less than about 1200 kPa absoluteand preferably from about 600 to about 900 kPa absolute. Hightemperatures tend to decrease the useful life of selective membranes.Accordingly, the temperature of the aqueous combination introduced intothe ultra-filtration membrane separation unit 300 is generally fromabout 20° C. to about 100° C., and typically from about 30° C. to about60° C. or from about 30° C. to about 50° C. If necessary, the aqueouscombination can be cooled prior to being introduced into membraneseparation unit 300 by methods conventionally known in the artincluding, for example, indirect heat exchange with other processstreams or with cooling water (e.g., as part of the quench step).

In order to maintain or enhance membrane separation efficiency andpermeate flux, the membranes should be periodically cleaned so as toremove contaminants from the surface of the membrane. Suitable cleaningincludes cleaning-in-place (CIP) operations wherein the surface of themembrane is exposed to a cleaning solution while installed withinultra-filtration unit 300 and nano-filtration unit 500. Some systemsmonitor the conductivity of the permeate, as conductivity can becorrelated to the concentration of components that pass through themembrane. An increase in conductivity in the permeate may indicate anincrease in transmission of the desired retentate compounds through themembrane and can be used to signal the need for cleaning operations.Additionally, a fall in permeate flow with all other factors remainingconstant may indicate fouling and the need for cleaning operations.Cleaning protocols and cleaning solutions will vary depending on thetype of separation membrane employed and are generally available fromthe membrane manufacturer. In order to not damage the membranes andunnecessarily shorten membrane life, the CIP operation is preferablyconducted using a solution of a standard pH at pressure and temperatureconditions known to those skilled in the art. In some applications, itmay be advantageous to conduct a cleaning operation on new separationmembranes prior to use in the membrane separation operation in order toimprove membrane performance.

The nano-filtration permeate stream 811 is delivered to an optionalcatalyst recovery unit 600. For example, catalyst recovery unit 600 maycomprise an ion exchange unit designed, for example when HCl or H₂SO₄ isthe catalyst, to capture the residual chloride or sulfate ions on theexchange resin prior to further processing to recover the HMF product.Ultimately, not more than about 10%, and typically not more than about5%, or not more than about 1% of the unconverted fructose and reactionintermediates are contained in the liquid fed via 811 to the ionexchange unit 600. Upon effecting ion exchange to capture substantiallyall of the remaining catalyst, the “catalyst free” eluent from the ionexchange unit 600 is supplied via 813 to a solvent separator 700 forseparating the solvent and a portion of the water from the product. Forexample, a flash evaporation unit may be utilized to vaporize thesolvent and some water, preferably essentially only the solvent. Thebottoms fraction, now comprised of primarily HMF and water can bewithdrawn via 815.

Separated solvent from solvent separator 700 is recovered in 814. Stream814 optionally provides diluent for nano-filtration unit 500 via 816.The remainder of the stream is supplied to the water removal unit 800via 814 a. A portion (preferably, substantially all) of the water instream 814 a can be removed as stream 817 employing of a number ofmethods including, but not limited to, distillation, adsorption,pervaporation and membrane separation. The water-reduced stream 818containing primarily solvent is supplied to mixer 100 for recycle toreaction zone 200.

The process described by FIG. 8 contains solvent separator unit 700which can be used to remove solvent and produce stream 815 containingHMF and water. In an alternative embodiment, unit 700 may configured toremove water via stream 814 (either as a pure water stream or as anazeotrope with the solvent) producing stream 815 containing HMF andsolvent, which may optionally contain some water.

While the various process schemes illustrated in the accompanyingFigures provide for a product containing HMF as an aqueous solution, itwill be evident to one of skill in the art that any of the processschemes may be readily adapted to produce HMF dissolved in a solventother than water, or HMF dissolved in a solvent/water combination.

EXAMPLES

The following non-limiting examples are provided to further illustratethe present invention.

Example 1

Fructose, water, HCl, NaCl and organic solvent were combined in a sealedreactor in the proportions detailed in Table 1. The reactor was heatedwith stirring to the temperature and for the time reported in Table 1.On cooling, samples of all layers were taken and the products wereanalyzed and composition determined by HPLC. HPLC analysis in Examples 1through 6 was conducted on an Agilent 1200 LC system using a ThermoScientific Hypercarb, 3.0×30 mm, 5 um column (guard) and an AgilentZorbax SB-Aq 3.0×100 mm, 3.5 um column (analytical) at 46° C. Thespecies were eluted under isocratic conditions of using a mixture of 90%(v/v) solvent mixture A (0.1% formic acid in water) and 10% (v/v)solvent mixture B (0.1% formic acid in 50:50 methanol:water) at a flowrate of 1.0 mL/min. Fructose, glucose and intermediates were detectedusing a universal charged aerosol detector (CAD), while HMF was detectedby UV at 254 nm. Fructose, glucose and HMF were quantified by fitting tocalibration curves generated from pure standards. Intermediates werequantified using a calibration curve generated from a structurallyrelated compound. The distributions of products are described in Table1.

TABLE 1 Total Sum of mol % Solvent Run Run Unconverted Fructose +Fructose HCl Water Added NaCl Temp. Time Fructose Intermediates HMFIntermediates + Entry wt % mol % wt % Solvent (mL) (mg) (° C.) (min) mol% mol % mol % HMF 1 20 5 20 2Butanol 4 130 120 30 35 16 49 100 2 20 5 202-Butanol 4 0 140 15 29 20 47 96 3 10 5 15 Diglyme 4 0 100 60 26 26 4395 4 10 10 15 Diglyme 4 0 100 30 26 26 43 94 5 10 20 15 Diglyme 4 0 10015 30 21 43 94 6 10 10 20 Diglyme 4 0 100 60 36 20 41 97 7 10 10 20Diglyme 4 0 100 60 37 20 42 99 8 10 15 20 Diglyme 4 0 100 30 33 24 41 999 10 5 20 Dioxane 2 0 130 15 35 19 46 100 10 10 5 20 Dioxane 2 0 140 1545 13 41 100 11 15 10 15 Glyme 4 0 110 30 26 23 48 97 12 20 5 20 Glyme 40 140 20 30 25 43 98 13 10 5 20 Glyme 2 0 140 15 32 19 48 99 14 30 1 20Glyme 4 0 160 30 29 23 43 95 15 10 5 20 THF 2 0 140 30 35 9 44 88

Example 2

13.0 g of HFCS-90 (77.2% DS, 93.7% fructose, 4.1% glucose, 2.2% DP2+),3.3 mL of 1 M aq. HCl, 12.6 mL of water, and 80.8 mL of dimethoxyethane(DME) were combined in a sealed container and heated with stirring at120° C. for 60 minutes. On cooling, a sample was taken and analyzed byHPLC for fructose+glucose, reaction intermediates, and HMF. HMF yield(based on total sugars): 48%; sum of unconverted fructose+mol % yield ofintermediates+mol % yield of HMF: 99%.

Example 3

10 g of fructose (56 mmol fructose), 3.3 mL of 1 M aq. HCl (3.3 mmolHCl), 18 mL of water, and 80 mL of dimethoxyethane (DME) were combinedin a sealed container and heated with stirring at 150° C. for 65minutes. The solution was cooled and the DME was removed by vacuumrotary evaporation. To the resulting aq. solution was added 60 mL ofmethyl isobutyl ketone (MIBK) and the mixture was stirred vigorously andallowed to phase separate. Samples from each layer were taken andanalyzed by HPLC for fructose, reaction intermediates, and HMF. HMFyield (based on fructose): 36%; sum of unconverted fructose+mol % yieldof intermediates+mol % yield of HMF: 98%. Table 2 reports thedistribution of the reaction constituents (fructose, reactionintermediates and HMF) in the different layers (phases).

TABLE 2 Volume Fructose Intermediates HMF Layer (mL) mol % mol % mol %Top 59  0%  0% 90% Bottom 9 100% 100% 10%

Example 4

120 g of fructose (666 mmol fructose), 33 mL of 1 M aq. HCl (33 mmolHCl), 67 mL of 5 M aq. NaCl (333 mmol NaCl), and 400 mL of 2-BuOH(1^(st) solvent) were combined in a sealed container and heated withstirring at 120° C. for 45 minutes. On cooling to room temperature, 50mL of hexane (2^(nd) solvent) was added, the mixture was stirredvigorously, and allowed to separate. Samples from each layer were takenand analyzed by HPLC for fructose, reaction intermediates, and HMF. HMFyield (based on fructose): 30%; sum of unconverted fructose+mol % yieldof intermediates+mol % yield of HMF: 93%. Table 3 reports the molefractions of reaction constituent (fructose), intermediates and productin the different layers (phases).

TABLE 3 Volume Moles reaction Layer (mL) Moles fructose intermediatesMoles HMF Top 544 0.021 0.00  0.181 Bottom 170 0.259 0.141 0.022

Example 5

To the bottom layer of Example 4 was added 45 g fructose (242 mmolfructose), 29 mL of 1 M aq. HCl (29 mmol HCl), and 400 mL of 2-BuOH. Themixture was heated with stirring in a sealed container at 120° C. for 45minutes. On cooling to room temperature, 50 mL of hexane was added, themixture was stirred vigorously, and allowed to separate. Samples fromeach layer were taken and analyzed by HPLC for fructose, reactionintermediates, and HMF. HMF yield (based on fructose +reactionintermediates): 32%; sum of unconverted fructose+mol % yield ofintermediates+mol % yield of HMF: 93%. Table 4 reports the molefractions of reaction constituent (fructose), intermediates and productin the different layers (phases).

TABLE 4 Volume Moles reaction Layer (mL) Moles fructose intermediatesMoles HMF Top 585 0.027 0.00  0.210 Bottom 159 0.230 0.139 0.021

Example 6

In this Example, commercially available acid-functionalized polymericion exchange resins were tested for fructose dehydration to HMF usingthe following catalyst testing protocol.

Catalyst was weighed into a glass vial insert followed by addition of300-1000 μl of 5 wt % fructose, fructose+glucose and/or InvertoseHFCS-90 solution plus solvent (5:1 organic solvent to water). The glassvial insert was loaded into a reactor and the reactor was closed. Theatmosphere in the reactor was replaced with nitrogen and pressurized to300 psig at room temperature. Reactor was heated to 120° C. andmaintained at 120° C. for 30-120 minutes while vials were shaken. Afterthe specified reaction time, shaking was stopped and the reactor wasrapidly cooled to 40° C. Pressure in the reactor was then slowlyreleased. The solutions were diluted with water and analyzed by liquidchromatography with CAD and UV detection and gas chromatography withflame ionization detection. The particulars of a variety of runs usingthe catalysts are reported in Table 5. For entries 6, 7 and 9, whichutilized solutions comprised of fructose with 10-20% glucose by weight,mol % unconverted fructose reported in Table 5 reflects the amount offructose+glucose within the reaction solution at time of quench.

TABLE 5 Sum of unconverted Reaction Run Unconverted Fructose + H+Catalyst Volume Time Fructose Intermediates HMF Intermediates + EntrySubstrate Resin (meq/g) (mg) (ul) Solvent (min) mol % mol % mol % HMF  1Fructose Amberlyst 15 4.85 10 400 Glyme 30 34 10 49 94  2 FructoseAmberlyst 15 4.85 9 500 Glyme 30 40 12 42 95  3 Fructose Amberlyst 154.85 9 750 Glyme 30 49 12 31 92  4 Fructose Purolite 275 DR 4.26 10 500Glyme 30 36 11 45 92  5 Fructose Purolite 275 DR 4.26 4 1000 Glyme 12050 0 45 95  6 Invertose Purolite 275 DR 4.26 7 400 Glyme 30 44 11 42 97HFCS-90  7 Fructose + Purolite 275 DR 4.26 7 400 Glyme 30 45 8 39 92Glucose (4:1)  8 Fructose Purolite 275 DR 4.26 9 750 Glyme 30 48 12 3494  9 Fructose + Purolite 275 DR 4.26 6 600 Glyme 30 54 12 30 96 Glucose(9:1) 10 Fructose Purolite 275 DR 4.26 7 600 Glyme 30 49 13 36 97 11Fructose Purolite 275 DR 4.26 4 600 IPA 120 40 2 49 90 12 FructosePurolite 275 DR 4.26 11 400 IPA 30 41 8 42 91 13 Fructose Purolite 275DR 4.26 5 1000 IPA 120 52 0 37 90

Example 7

In this example, high fructose corn syrup was converted to HMF in acontinuous flow reactor.

The flow reactor consisted of a 0.25″×73″ zirconium tube having anapproximate volume of 30.0 mL. The reactor tube was vertically mountedin an aluminum block heater equipped with PID controller. Feed solutionswere delivered in upflow mode using two HPLC pumps and the reactorpressure was controlled at 300 psi by means of a back pressureregulator.

Two feed solutions were prepared, Feed 1: 10 wt % HFCS-90, dissolved inDioxane/H₂O (4/1 by volume); and Feed 2: 10 wt % HFCS-90, 0.12 wt % HCldissolved in Dioxane/H₂O (4/1 by volume).

The reaction was performed at 120° C. with a fixed residence time of 5minutes and a total feed flow rate of 6 mL/min. Reaction conversion wascontrolled by varying the amount of HCl through changes in the flowratio of Feed 1 and Feed 2. Reaction progress was monitored and productcomposition was determined by HPLC analysis on a Thermo Ultimate 3000analytical chromatography system using a porous graphitic stationaryphase (Hypercarb, 3.0>100 mm, 5 um) at 30° C. Fructose and glucose wereeluted under isocratic conditions of 0.005% v/v NH₄OH in H₂O at a flowrate of 0.6 mL/min. Intermediates and 5-(hydroxymethyl)furfural (HMF)were eluted by employing a gradient of up to 60% MeOH at a flow rate of1.0 mL/min. Fructose, glucose and intermediates were detected using auniversal charged aerosol detector (CAD) and HMF was detected by UV at254 nm. Fructose, glucose, and HMF were quantified by fitting tocalibration curves generated from pure standards. Intermediates werequantified using a calibration curve generated from a structurallyrelated reference compound. The results are summarized in the Table 6below and the data from this example is depicted graphically in FIG. 9.

TABLE 6 Sum of mol fraction % of unconverted Fructose + Unconverted mol% wt % Fructose Glucose Intermediates HMF Intermediates + HCl mol % mol% mol % mol % mol % HMF 0.00 90% 10% 0%  0% 100% 0.01 31% 10% 4% 47% 91% 0.02 24% 10% 3% 57%  94% 0.04  8% 10% 2% 71%  91% 0.06  9% 10% 1%74%  94% 0.08  3%  9% 1% 75%  88% 0.10  3%  9% 0% 76%  88%

Example 8

In this example, ultra-filtration and nano-filtration membranes wereused to remove humins from the aqueous product effluent resulting fromconversion of fructose to HMF.

Product effluent for testing of ultra- and nano-filtration was producedunder conditions analogous to those described in Example 7, but using1,2-dimethoxyethane (DME) as the solvent (4/1 DME/water by volume). Thispartial conversion continuous flow process gave an aqueous productmixture consisting of 24 mol % fructose, 8 mol % glucose, 9 mol %intermediates, 56 mol % HMF and 3 mol % unidentified oligomeric orpolymeric materials referred to as humins.

The HCl in the collected product effluent was neutralized with 1 eq ofNaOH prior to removal of DME by rotary evaporation. The remaining crudeaqueous product mixture was diluted 3.8 times by volume with deionizedwater and subjected to ultra-filtration and nano-filtration treatmentfor removal of humins.

In one test, cross-flow ultra-filtration was performed by circulating 2L of the opaque dark brown aqueous product mixture through a 2.7 m²spiral wound GE UF membrane having a molecular weight cut-off (MWCO) of1000 available from GE Water & Process Technologies, Inc. After 4.25minutes, the collected permeate was analyzed by HPLC. Fructose, glucose,HMF, and intermediates all passed through the membrane while a majorityof the colored bodies (humins) did not and remained in the retentate.The collected permeate was a clear orange solution.

In another test, cross-flow nano-filtration was performed by circulating1 L of the opaque dark brown aqueous product mixture through a 2.7 m²spiral wound Dairy NF membrane having a MWCO of 150 available from GEWater & Process Technologies, Inc. After 3.8 minutes, the collectedpermeate was analyzed by HPLC. The permeate consisted of HMFsubstantially free of fructose, glucose, intermediates, and coloredbodies (humins). The collected permeate was a clear pale yellowsolution.

In another test, cross-flow filtration was performed by circulating 1 Lof the opaque dark brown aqueous product mixture through a 2.6 m² spiralwound H series membrane having a MWCO of 150-300 available from GE Water& Process Technologies, Inc. After 20.0 minutes, the collected permeatewas analyzed by HPLC. The permeate consisted primarily of HMF with avery small amount of fructose and no detectable quantity of glucose orintermediates. The colored bodies (humins) were substantially removed.The collected permeate was a clear pale yellow solution.

When introducing elements of the present invention or the preferredembodiments(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to mean that theremay be additional elements other than the listed elements.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above processes and productswithout departing from the scope of the invention, it is intended thatall matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A process for the production of a productcomprising 5-(hydroxymethyl)furfural (HMF) and water, the processcomprising: combining fructose, water, a homogeneous acid catalyst andat least a first solvent in one or more reaction zones; converting inthe one or more reaction zones a portion of the fructose to HMF andwater; removing from at least one of the reaction zones a combinationcomprising at least a portion of the HMF, humins, homogeneous acidcatalyst and first solvent; neutralizing the homogeneous acid catalystby addition of a base to the combination; and contacting the neutralizedcombination with one or more selective membranes to produce a retentatecomprising humins and a permeate depleted in humins and comprising HMF.2. The process of claim 1 wherein the combination further comprisesunconverted fructose and intermediates to HMF, the retentate furthercomprises unconverted fructose and intermediates and the permeate isdepleted in unconverted fructose and intermediates.
 3. The process ofclaim 1 wherein the one or more selective membranes are selected fromultra-filtration membranes, nano-filtration membranes, and combinationsthereof.
 4. The process of claim 3 wherein the one or more selectivemembranes comprises ultra-filtration membranes.
 5. The process of claim1 wherein the solids content of the combination withdrawn from thereaction zone is reduced prior to contacting the combination with one ormore selective membranes.
 6. The process of claim 5 wherein the solidscontent of the combination withdrawn from the reaction zone is reducedby dilution with an aqueous diluent.
 7. The process of claim 5 whereinthe solids content of the combination withdrawn from the reaction zoneis reduced by filtration.
 8. The process of claim 5 wherein the solidscontent of the combination withdrawn from the reaction zone is reducedto less than about 1000 ppm.
 9. The process of claim 1 wherein the oneor more selective membranes are in a cross-flow arrangement.
 10. Theprocess of claim 1 wherein the one or more selective membranes are in asingle pass system.
 11. The process of claim 1 wherein the one or moreselective membranes are in a multi-pass system.
 12. The process of claim1 wherein the one or more selective membranes have a geometry selectedfrom the group consisting of flat, tubular, capillary, and spiral-wound.13. The process of claim 1 wherein the homogenous acid catalyst isselected from the group consisting of mineral acids, organic acids, andcombinations thereof.
 14. The process of claim 13 wherein the homogenousacid catalyst is selected from the group consisting of HCl, HBr, HI,H₂SO₄, HNO₃, H₃PO₄, oxalic acid, CF₃SO₃H, CH₃SO₃H, borontrihalides, andcombinations thereof.
 15. The process of claim 14 wherein the homogenousacid catalyst is selected from the group consisting of HCl, HBr, H₂SO₄,H₃PO₄, and combinations thereof.
 16. The process of claim 15 wherein theacid catalyst comprises HBr.
 17. The process of claim 1 wherein thecombination is mono-phasic.
 18. A process for the production of aproduct comprising 5-(hydroxymethyl)furfural (HMF) and water, theprocess comprising: combining fructose, water, an acid catalyst and atleast a first solvent in one or more reaction zones; converting in theone or more reaction zones a portion of the fructose to HMF and waterand to intermediates to HMF; removing from at least one of the reactionzones a combination comprising at least a portion of the HMF,unconverted fructose, intermediates, humins, and first solvent,contacting the combination with one or more ultra-filtration membranesto produce a retentate comprising humins and a permeate depleted inhumins that comprises unconverted fructose, intermediates, HMF, firstsolvent, and water; and contacting the ultra-filtration permeate withone or more nano-filtration membranes to produce a retentate comprisingunconverted fructose and a permeate substantially free of unconvertedfructose and comprising HMF.